1. Field of the Invention
The present invention relates to a numerical controller for a grinding machine capable of successively grinding a plurality of workpieces or axially spaced portions of a workpiece in accordance with a numerical control program.
2. Discussion of the Prior Art
In successively grinding workpieces in a numerical control cylindrical grinding machine, the diameter of a finished portion of a first workpiece is measured for the difference from a commanded diameter after the first workpiece is machined in accordance with a numerical control program. The difference is then used to modify plunge inwheel feed position data in the numerical control program so that a second workpiece and other workpieces successive thereto can be precisely machined to the commanded diameter. In this method, the first workpiece cannot be machined to the commanded diameter and as the case may be, has to be machined again in a manual feed mode.
To avoid this drawback, in a numerical control grinding machine, an automatic operation is halted in mid course of machining, and the operational mode of the machine is switched to a manual mode to retract a grinding wheel and then, to measure the diameter of the workpiece. Thereafter, the grinding wheel is returned to a previous infeed end position, and the position of the grinding wheel is then adjusted by a size error which can be calculated based upon the grinding wheel position and the measured diameter of the workpiece. The automatic operation is resumed upon completion of the position adjustment, so that the workpiece can be machined to a desired finish diameter.
Although in the known grinding machine, the desired finish diameter can be obtained even on a first machined workpiece, there are involved various drawbacks noted below. That is, the determination of a timing at which the automatic operation is to be halted depends on the operator, who is thus required to observe the machining operation of the first workpiece. Further, where the workpiece has a plurality of axially stepped portions which are to be successively machined in accordance with a numerical control program, revision has to be made with plunge infeed control data for all of the workpiece portions prior to the machining of a second workpiece portion, and such revision is in fact complicated and troublesome.
In addition, known numerical controllers are usually provided with one active register and two buffer registers. Thus, when a grinding operation is performed in accordance with a numerical control data block being stored in the active register, two numerical control data blocks successive to that in the active register have already been stored in the buffer registers. Consequently, after the revision of a numerical control program stored in a memory device, the data blocks in the buffer registers have to be replaced with those revised and corresponding thereto. To this end, prior to resumption of the automatic machining operation, the operator is required to search for the revised data blocks corresponding to those in the buffer registers and then, to load the searched revised data blocks in the buffer registers in place of those already therein. These manipulations by the operator make the subsequent resumption of the automatic machining operation difficult and provide a larger chance to involve errors.